1. Field of the Invention
The present invention pertains to a method and apparatus for plugging and abandoning wells, such as oil and/or gas wells. More particularly, the present invention pertains to a method and apparatus for mechanically cutting and removing tubular goods including, but not limited to, casing from wells without requiring use of a drilling rig, workover rig or other similar equipment.
2. Description of the Prior Art
Wells, such as oil and gas wells, are typically drilled using drilling rigs or other similar systems. In most cases, drilling rigs are used to drill substantially cylindrical boreholes downward into the earth's crust. Once a well has been drilled to a desired depth, large diameter pipe commonly referred to as casing is thereafter installed into a well and cemented in place. Casing is typically installed to provide structural integrity to a borehole and to keep geologic formations (as well as any fluids contained therein) isolated from one another.
In many cases, a single well can have multiple strings of casing. In such cases, a first casing string having a relatively large inner diameter and corresponding outer diameter is driven into the earth's crust. Thereafter, a length of borehole is drilled from said first casing string. A second, smaller casing string is concentrically installed within said first casing string and bore hole and cemented in place. This process can be repeated until a well is drilled to a predetermined depth and a desired length of casing is installed in such well. In most cases, once a well is drilled to its desired depth, production tubing is concentrically installed within the innermost casing string, and surface equipment is erected.
It is frequently challenging and expensive to plug and abandon wells after hydrocarbon reserves in such wells have been depleted. Generally, surface equipment and production tubing must first be removed from a well. Thereafter, as much casing as possible is typically retrieved from the well; in many cases, such casing can be reused in other wells or sold for salvage. However, because the casing (or large portions thereof) is typically cemented in place, blades or other cutting devices are frequently required to cut the casing at a desired depth in the well.
After desired cut(s) are made, the casing is typically pulled out of the well from the surface. However, due to the weight of the pipe, as well as frictional forces acting on such pipe, it is often difficult to pull the casing out of the well. Accordingly, pulling equipment, such as hoists, jacks or the like, are often required to pull the casing out of a well.
Drilling rigs and smaller work-over rigs are frequently used to plug and abandon wells. A rig's rotary equipment can be utilized to actuate blades and/or other cutting equipment in order to make down-hole cuts in a casing string. Further, a rig's derrick and draw works can also be used to pull casing from a well. However, drilling rigs, which are typically leased to well owners on a daily basis, can be expensive to use for abandonment operations. Moreover, drilling rigs can also be difficult and expensive to mobilize, especially when such rigs are intended to work on offshore wells drilled from platforms or other marine structures.
Systems have been developed for plugging and abandoning wells without the use of a drilling or workover rig. However, existing “rig-less” tubular removal systems have some significant shortcomings.
Existing rig-less tubular removal systems generally utilize a power swivel that is supported over a well bore. In such cases, the power swivel is used to rotate a string of pipe at the surface that, in turn, causes blades or other cutting devices to rotate downhole. A crane is typically utilized to support axial loading on the power swivel, while a snub line or “dead man” is typically used to offset radial loading on the power swivel.
With existing rig-less tubular removal systems, power swivels are frequently not adequately supported or stabilized. As a result, power swivels can often move and sway radically during operation. When a power swivel sways at the surface, such movement is frequently transferred down hole to blades or other cutting devices within a well bore. Such movement can cause the blades or other cutting devices to change positions within a well bore which, in turn, can change the depth at which casing or other tubular goods are cut.
Even if a power-swivel is not moving or swaying radically at the surface, existing systems permit downhole travel of cutting blades. When a power swivel is not firmly supported and secured, as is frequently the case with existing tubular removal systems, the position of downhole cutting blades can change over time. This results in longer cutting times and, frequently, increased damage to downhole blades. Further, when multiple strings of casing are cut in extended reach applications having large diametric variance, downhole cutting operations become extremely difficult, if not impossible, using existing tubular removal systems.
Ultimately, such lack of support and stability of a power swivel affects the depth at which tubulars are cut which, in turn, impacts the amount of tubulars that can be recovered from a well. If a cut is made too shallow, excess pipe can be left in a well. Alternatively, if a cut is made too deep, the length of pipe to be pulled out of the well can be greater than anticipated and can exceed the load capacity of a crane or other hoisting means.
Significant time and effort is required to rig up and rig down existing rig-less tubular removal systems. With such existing systems, a power swivel must generally be rigged down and rigged back up between each cut, even on multi-well platforms or other marine structures. Rigging up of a power swivel typically requires connecting a hydraulic power pack (engine and pumps) to the swivel head of the power swivel using a number of different hoses. Thereafter, the power swivel is typically picked up with one line of a crane, while another line of a crane is used to “snub off” the power swivel to some fixed point on the platform utilizing a torque arm or dead man connected to the swivel head. Rigging down the power swivel entails the same basic process in reverse order, except that the power swivel must be stored in an alternate location during such operation.
Existing rig-less tubular removal systems also give rise to safety concerns. One such safety concern results from repeated stretching and relaxing of crane cables during cutting operations. Such loading can cause the cables to fatigue, thereby making such cables more susceptible to breaking. For example, if a snub line breaks, the power swivel can spin and bounce wildly. If this occurs, connecting hoses will typically break, spewing hydraulic oil and/or other fluids around the work site and surrounding environment.
Additionally, if downhole cutting blades become lodged, or if the cut casing or tubulars fall onto the blades, a crane is typically unable to pull such blades free. Even if the blades can be pulled free, the power swivel will frequently bounce upward at the surface in response to such blades coming free. Under either scenario, personnel in the vicinity of the operation are placed at risk.
Thus, there is a need for a method and apparatus for mechanically plugging and abandoning wells, especially wells drilled from offshore platforms or other marine structures, that is safer and more effective than existing systems.